1. The basic requirements of SMT process for component layout design are as follows:
The distribution of the components on the printed circuit board should be as uniform as possible. The heat capacity of reflow soldering of large quality components is large, and excessive concentration is easy to cause local low temperature and lead to virtual soldering. At the same time, the uniform layout is also conducive to the balance of the center of gravity. In vibration and impact experiments, it is not easy to damage the components, metallized holes and solder pads.
2. The alignment direction of the components on the printed circuit board should be the same as far as possible for similar components, and the characteristic direction should be the same to facilitate the installation, welding and detection of the components. If electrolytic capacitor positive pole, diode positive pole, transistor single pin end, the first pin of integrated circuit arrangement direction is consistent as far as possible. The printing direction of all component numbers is the same.
3. Large components should be left around the SMD rework equipment heating head can be operated size.
4. Heating components should be as far away from other components as possible, generally placed in the corner, box ventilation position. Heating components should be supported by other leads or other supports (such as heat sink) to keep a certain distance between the heating components and the printed circuit board surface, with a minimum distance of 2mm. Heating components connect the heating components with printed circuit boards in multilayer boards. In design, metal solder pads are made, and in processing, solder is used to connect them, so that the heat is emitted through printed circuit boards.
5. Temperature-sensitive components should be kept away from heat-generating components. Such as audions, integrated circuits, electrolytic capacitors and some plastic case components, should be as far away from the bridge stack, high-power components, radiators and high-power resistors.
6. The layout of components and parts that need to be adjusted or often replaced, such as potentiometers, adjustable inductance coils, variable capacitor micro-switches, insurance tubes, keys, plugers and other components, should consider the structural requirements of the whole machine, and place them in a position that is easy to adjust and replace. If the machine adjustment, should be placed on the printed circuit board to facilitate adjustment of the place; If it is adjusted outside the machine, its position should be adapted to the position of the adjusting knob on the chassis panel to prevent the conflict between three-dimensional space and two-dimensional space. For example, the panel opening of the button switch should match the position of the switch vacancy on the printed circuit board.
7. A fixed hole should be set near the terminal, plug and pull parts, the central part of the long terminal and the part that is often subjected to force, and a corresponding space should be left around the fixed hole to prevent deformation due to thermal expansion. Such as long terminal thermal expansion is more serious than printed circuit board, wave soldering prone to warping phenomenon.
8. For some components and parts (such as transformers, electrolytic capacitors, varistors, bridge stacks, radiators, etc.) with large tolerance and low precision, the interval between them and other components should be increased by a certain margin on the basis of the original setting.
9. It is recommended that the increase margin of electrolytic capacitors, varistors, bridge stacks, polyester capacitors and other capacitors should be no less than 1mm, and that of transformers, radiators and resistors exceeding 5W (including 5W) should be no less than 3mm
10. The electrolytic capacitor should not touch the heating components, such as high-power resistors, thermistors, transformers, radiators, etc. The interval between the electrolytic capacitor and the radiator should be a minimum of 10mm, and the interval between other components and the radiator should be a minimum of 20mm.
Post time: Dec-09-2020